Leaders of the Association of Southeast Asian Nations made the decision during their annual summit in the Cambodian capital of Phnom Penh, ASEAN Secretary-General Surin Pitsuwan said.

The South China Sea territorial disputes, which many fear could spark Asia’s next war, have overshadowed discussions at the summit, where the top agenda items included human rights and expanding an Asian free-trade area.

Four countries in the 10-member ASEAN — Brunei, Malaysia, the Philippines and Vietnam — have been locked in long-unresolved territorial rifts with China and Taiwan in the resource-rich waters, where a bulk of the world’s oil and cargo passes.

Since Chinese and Vietnamese naval forces engaged in deadly clashes in the region in the 1970s, the disputes have settled into an uneasy standoff.

But fresh territorial spats involving China, Vietnam and the Philippines starting last year have set off calls for ASEAN and China to turn a nonaggression accord they signed in 2002 to a stronger, legally binding “code of conduct” aimed at discouraging aggressive acts that could lead to dangerous confrontations or accidental clashes in the busy region.

ASEAN member countries have submitted features they each want to see in such an accord, and now are ready to sit as a bloc to discuss with China how the agreement could be drafted. The crucial talks could start immediately, even right after the Cambodia summit, according to Mr. Surin.

Cambodian Prime Minister Hun Sen, host of this year’s summit, would convey the bloc’s decision to his Chinese counterpart, Wen Jiabao, who would fly to Cambodia later Sunday to join expanded ASEAN meetings in the next two days.

“They would like to see the commencement of the discussion as soon as possible because this is an issue of interest, concern and worry of the international community,” Mr. Surin told reporters. “It’s an issue between ASEAN and China to resolve together It needs two to tango.”

President Obama also would fly to Cambodia to attend on Tuesday the so-called East Asia Summit, an annual forum where ASEAN leaders and their counterparts from eight other nations, including China and the United states, would discuss security and economic concerns. Washington has backed calls for the drafting of a South China Sea nonaggression pact.

It’s unclear how China would respond, with ASEAN diplomats saying they have gotten unclear signals from Chinese officials.

Vietnam and the Philippines separately have accused China since last year of intruding into South China Sea islands, reefs and waters they claim and of disrupting their oil explorations well within their territorial waters.

China, which claims virtually the entire South China Sea, has dismissed the protests, saying those waters belonged to Beijing since ancient times.

China has sought one-on-one negotiations with rival nations to resolve the disputes, something that will give it advantage because of its sheer size, and has objected to any effort to bring the problem to regional or international forums such as ASEAN.

Beijing also has warned Washington not to get involved, but American officials have declared that the peaceful resolution of the disputes and freedom of navigation in the vast sea was in the U.S. national interest.

Mr. Obama is expected to reiterate Washington’s call for a legally binding code of conduct in the South China Sea in Cambodia.

Meanwhile, ASEAN leaders adopted a human rights declaration on Sunday despite last-minute calls for a postponement by critics, including Washington, who said the pact contains loopholes that can allow atrocities to continue.

ASEAN, an unwieldy collective of liberal democracies and authoritarian states, signed a document adopting the Human Rights Declaration in Phnom Penh. The nonbinding declaration calls for an end to torture, arbitrary arrests and other rights violations that have been longtime concerns in Southeast Asia, which rights activists once derisively described as being ruled by a “club of dictators.”